Astrophys. J., 868, 30-30 (2018/November-3)
The dynamical mass and evolutionary status of the Type II Cepheid in the eclipsing binary system OGLE-LMC-T2CEP-211 with a double-ring disk.
PILECKI B., DERVISOGLU A., GIEREN W., SMOLEC R., SOSZYNSKI I., PIETRZYNSKI G., THOMPSON I.B. and TAORMINA M.
Abstract (from CDS):
We present the analysis of a peculiar W Virginis (pWVir) type II Cepheid, OGLE-LMC-T2CEP-211 (Ppuls = 9.393 days), in a double-lined binary system (Porb = 242 days), which shed light on virtually unknown evolutionary status and structure of pWVir stars. The dynamical mass of the Cepheid (first ever for a type II Cepheid) is 0.64 ± 0.02 M☉, and the radius R = 25.1 ± 0.3 R☉. The companion is a massive (5.67 M☉) main-sequence star obscured by a disk. Such a configuration suggests a mass transfer in the system history. We found that originally the system (Porbinit = 12 days) was composed of 3.5 and 2.8 M☉ stars, with the current Cepheid being more massive. The system age is now ∼200 Myr, and the Cepheid is almost completely stripped of hydrogen, with helium mass of ∼92% of the total mass. It finished transferring the mass 2.5 Myr ago and is evolving toward lower temperatures passing through the instability strip. Comparison with observations indicates a reasonable 2.7 x 10–8 M☉ yr–1 mass loss from the Cepheid. The companion is most probably a Be main-sequence star with T = 22,000 K and R = 2.5 R☉. Our results yield a good agreement with a pulsation theory model for a hydrogen-deficient pulsator, confirming the described evolutionary scenario. We detected a two-ring disk (Rdisk ∼ 116 R☉) and a shell (Rshell ∼ 9 R☉) around the companion, which is probably a combination of the matter from the past mass transfer, the mass being lost by the Cepheid owing to wind and pulsations, and a decretion disk around a rapidly rotating secondary. Our study, together with observational properties of pWVir stars, suggests that the majority of them are products of a similar binary evolution interaction.
© 2018. The American Astronomical Society. All rights reserved.
binaries: eclipsing - circumstellar matter - galaxies: individual: LMC - stars: emission-line, Be - stars: evolution - stars: variables: Cepheids
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